Abstract

Based on the known linking options of their fundamental building unit, i.e. SiN4 tetrahedra, nitridosilicates belong to the inorganic compound classes with the greatest structural variability. Although facilitating the discovery of novel Si-N networks, this variability represents a challenge when targeting non-stoichometric compounds. Meeting this challenge, we report on a strategy for targeted creation of vacancies in highly condensed nitridosilicates by exchanging divalent M2+ by trivalent M3+ via the ion exchange approach. As proof of concept, the first Sc and U nitridosilicates were prepared from alpha-Ca2Si5N8 and Sr2Si5N8. Powder X-ray diffraction (XRD) and synchrotron single-crystal XRD showed random vacancy distribution in Sc0.2Ca1.7Si5N8 and partial vacancy ordering in U0.5xSr2-0.75xSi5N8 with x approximately 1.05. The high chemical stability of U nitridosilicates makes them interesting candidates for immobilization of actinides.